linux-kernel - Re: [PATCH v2 2/2] x86/mm/pat, drivers/media/ivtv: move pat warn and replace WARN() with pr

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Date:	Thu, 25 Jun 2015 08:51:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
Cc:	bp@...e.de, andy@...verblocksystems.net, mchehab@....samsung.com,
	dledford@...hat.com, fengguang.wu@...el.com,
	linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [PATCH v2 2/2] x86/mm/pat, drivers/media/ivtv: move pat warn and
 replace WARN() with pr_warn()


* Luis R. Rodriguez <mcgrof@...not-panic.com> wrote:

> From: "Luis R. Rodriguez" <mcgrof@...e.com>
> 
> On built-in kernels this warning will always splat as this is part
> of the module init. Fix that by shifting the PAT requirement check
> out under the code that does the "quasi-probe" for the device. This
> device driver relies on an existing driver to find its own devices,
> it looks for that device driver and its own found devices, then
> uses driver_for_each_device() to try to see if it can probe each of
> those devices as a frambuffer device with ivtvfb_init_card(). We
> tuck the PAT requiremenet check then on the ivtvfb_init_card()
> call making the check at least require an ivtv device present
> before complaining.
> 
> Reported-by: Fengguang Wu <fengguang.wu@...el.com> [0-day test robot]
> Signed-off-by: Luis R. Rodriguez <mcgrof@...e.com>
> ---
>  drivers/media/pci/ivtv/ivtvfb.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
> index 4cb365d..8b95eef 100644
> --- a/drivers/media/pci/ivtv/ivtvfb.c
> +++ b/drivers/media/pci/ivtv/ivtvfb.c
> @@ -38,6 +38,8 @@
>      Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
>   */
>  
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
>  #include <linux/module.h>
>  #include <linux/kernel.h>
>  #include <linux/fb.h>
> @@ -1171,6 +1173,13 @@ static int ivtvfb_init_card(struct ivtv *itv)
>  {
>  	int rc;
>  
> +#ifdef CONFIG_X86_64
> +	if (pat_enabled()) {
> +		pr_warn("ivtvfb needs PAT disabled, boot with nopat kernel parameter\n");
> +		return -ENODEV;
> +	}
> +#endif
> +
>  	if (itv->osd_info) {
>  		IVTVFB_ERR("Card %d already initialised\n", ivtvfb_card_id);
>  		return -EBUSY;

Same argument as for ipath: why not make arch_phys_wc_add() fail on PAT and return 
-1, and check it in arch_phys_wc_del()?

That way we don't do anything drastic, the remaining few drivers still keep 
working (albeit suboptimally - can be worked around with the 'nopat' boot option) 
- yet we've reduced the use of MTRRs drastically.

Thanks,

	Ingo
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